Key groundwater-well terms during pumping: Which combination of statements correctly describes water-level behavior, depression head (drawdown), cone of depression, and radius of influence around a pumped well?

Introduction / Context:
Pumping tests and well hydraulics use several standard terms to quantify aquifer response: drawdown (depression head), cone of depression, and radius of influence. A stilling well or observation well is used to monitor groundwater levels under near-still conditions to avoid dynamic fluctuations.

Given Data / Assumptions:

• Unconfined aquifer with an initially horizontal water table.
• Steady pumping causes water-level decline near the well.
• Observation points record levels for analysis.

Concept / Approach:
Drawdown equals static water level minus pumping water level. Spatial variation of drawdown creates a characteristic cone-shaped surface known as the cone of depression. Radius of influence is the distance from the well at which drawdown becomes negligible for practical purposes. A stilling/observation well reflects the ambient groundwater level (absent rapid dynamic disturbances).

Step-by-Step Solution:
Identify monitoring: stilling well tracks groundwater level reliably.Define drawdown: s = h_static - h_pumped.Conceptualize the cone of depression around the well.Define radius of influence: distance to near-zero drawdown.

Verification / Alternative check:
Log-log and semi-log analyses (e.g., Theis, Cooper–Jacob) utilize observation well drawdowns to estimate transmissivity and storativity, consistent with these definitions.

Why Other Options Are Wrong:
Each individual statement (A–D) is correct; the most complete choice is “All the above.” Selecting only one omits the integrated description of well hydraulics terms.

Common Pitfalls:

• Equating radius of influence with aquifer boundary; it is a practical extent of measurable drawdown.
• For confined aquifers, the potentiometric surface responds similarly even though the water table is not exposed.

Final Answer:
All the above